Since 1927, the surfactant flooding process has been the most prevalent method of achieving enhanced oil recovery from underground wells. Generally, easily recoverable oil is first removed from an underground reservoir, most commonly by water flooding. The enhanced recovery process is then performed to recover the remainder of the oil. Since so much water has been introduced into the well, the recovered product will generally contain a significant amount of water. To perform the enhanced recovery, surfactants are added to the reservoir to lower the surface tension between the water and oil contained therein. The surfactant recovery process results in a three-phase system, a top oil phase, a lower brine water phase, and a middle phase water and oil emulsion, the latter comprising about 40% of the total. Since significant amounts of oil and surfactants are contained in this middle phase emulsion, prior art attempts have been made to break the emulsion to recover the oil and surfactants therefrom.
Prior art methods of breaking middle phase emulsions are usually carried out by the addition of chemical demulsifiers to the emulsion. U.S. Pat. No. 4,029,570, issued June 14, 1977, discloses a method of breaking an oil-water-sulfonate middle phase emulsion by mixing the emulsion with brine, agitating the mixture, and separating the crude oil therefrom.
U.S. Pat. No. 4,261,812, issued Apr. 14, 1981, discloses a method of breaking an oil and water emulsion by adding additional surface active agents, preferably additional petroleum sulfonates, and subjecting the emulsion to traditional emulsion breaking techniques, such as the addition of brine. U.S. Pat. No. 4,374,734 discloses a similar process wherein the emulsion is treated with brine and a polyol or quaternary ammonium compound or both.
Some prior art methods of oil and water separation have involved physical methods. U.S. Pat. No. 4,071,438, issued Jan. 31, 1978, involves a method of reclaiming or re-refining waste oils involving a dehydrating step and a subsequent vacuum distillation step.
U.S. Pat. No. 3,840,468, issued Oct. 8, 1974, discloses a method for separating emulsions of waste oil and water by a falling-film evaporation process.
U.S. Pat. No. 4,370,238, issued Jan. 25, 1983, discloses a method for the removal of water from a surfactant containing crude oil comprising a water removal step, and a step to separate the oil from the surfactants wherein the oil is separated by an alcohol phase separation and the alcohol is then distilled so that surfactants may be recovered. However, none of the processes involving physical separation steps have been used to separate middle phase emulsions.
There remains a need in the art for an efficient and economical process to separate middle phase emulsions and recover the valuable components contained therein.